Method and apparatus for treating and filtering clay slip



July 28, 1936. D. F. M CORMICK 2,049,071

METHOD AND APPARATUS FOR TREATING AND FILTERING CLAY SLIP Original Filed May 12,1951 3 Sheets-Sheet l INVENTOR.

ATTORNEY July 28, 1936. MCCORMICK 2,049,071

METHOD AND APPARATUS FOR TREATING AND FILTERING CLAY SLIP Original Filed May 12, 1931 3 Sheets-Sheet 2 llmlllu' ATTORNEY July 28, 1936.

D. F. MCCORMICK METHOD AND APPARATUS FOR TREATING AND FILTERING CLAY SLIP Original Filed May 12, 1931 3 Sheets-Sheet INVENTOR a fin fmwf' BY T'E'ORNEY I Claims. n. 2 9.

The present application :is a divisionalapplication of my original application for Method of treating clay, SerialNo. 536,955ffi1ed May: 12, 1931. In that application I described and claimed methods of refiningrcrude clay by acombined dry and wet process whereby the removal of the impurities is facilitated and the resulting product is pure clay with substantially no waste. Upon 10 reference to said application, now Patent No. 1,930,247, issued Oct. 10, 1933, it will appear that several steps in the methods, .and apparatus for carrying out those steps, are described, and that they play an important part and contribute to the eficient handling of the product, and promote economy in power and increase in output. One of these steps and the apparatus for prac-' ticing same, relates to filtering the slip for. the recovery of the clay, as well as to the treatment 29 of the slip before filtering and to the treatment of the filter cake during formation and after discharge. The present applicationis directed to these features.

As outlined in my patent aforementioned, wet processes of refining clay have necessarily involved a. filtering step, wherein filter presses are employed and their necessary manipulation by hand, renders the entire operation sluggish and intermittent. Furthermore, the handling of these presses is uneconomical in time and labor,

and therefore retards the refining operation.

However, peculiar properties of clay have presented 'dimcult problems in the filtering field, j

Although uninterrupted or continuous filtering.

has met with success in various fields, the peculitrlties of the clay slip and the clay cake,

heretofore have presented problems which have o defied economical solution;

Thepresent improvements, therefore, have as their primary object, the provision of novel means and methods for treating clay slip before, during and after filtering, so as to present an efiicient 45 and continuous filtering method. The adaptation of certain conventional filtering means, for the emoient filtering of clay slip, constitutes a further object. 7

Anotherobject is to provide novel means and so methods for preheating the clay slip before it is subjected to the filtering step.

A further object of the improvements is to provide a novel type of filter unit having novel features of construction. Improved methods of $5 treating the slip and cake during filteringgconq stitute another object. 'Heating the continuous ly discharging filter' calie is 1 a: further fobjectxv Among other feature's, the present improve ments have for theiruobjectgitheifprovlsion "of. means for heating -andt-fdrying the ifilter: cake'as.-'r 5 it is being formed andsdewatere'd; This means; may take the former a' hoodzor' other' conduit means for directing heated air-:or gasessonto the rfilter drum. A further objectisto provideim-w' proved means and methodsi for'removing the clay cake from the filter. media; .so as to prevent r sticking V. A general-objectof 'the improvements is thenv provision of a filtering'me'ans: andmethod which 9' is successful, eiiicient andzeconomicalinthe-re 15 finement" of clay.

Otherobjects and advantagespwillhe apparent Y to thoseskilled in the'art'npon reference to they,

- accompanying specification and drawings,

bafiies and air conduit of Figure 1;

Figure 4 is a diagrammaticview of another modified form of conveyorand drier; i 1;

Figure 5 is an enlargeddetail of the mechanical scraper illustrated in Figured; V 1

Figure 6 is an enlarged detail of themechanicalscraper illustrated in Figure 4;

Referring to the dravvingsythe shell e15 .stacloii 3 (Fig. 1) is equipped with, stationary funnel shaped partitions 6 which cooperatewith rotary, 3 or stationary, conical discs or ,batfies Ti toprovide a cascade for the slip which isied to the top or C the cylinder through pipeii. The battles or. discs 40 l are mounted on shaft 9 driven by gears it and I wheel 9 I from any suitablepower source. It is not always necessary to revolvethese discs in which, case they'remain stationary. Thisrunit serves as,

a heat interchanger and for this purpose ahot 4 air conduit l2 empties into the lower end of the cylinder, the heated air and gases ascending the cascade and leaving by the flue. $3. It desired, the valves in conduits i3 and lSA. can be setsothat,

the heated air may beledthrough itA instead sit-gee 23 to a condenser 01' other unit for further use 5' with other unitsrso that-eventually only a saw. fraction of the heat employed is wasted l The conical base of the stack or cylinder 5 som municates with pipe M which leads to the tank drum I8. which may be of any suitable construc tion having a peripheral surface of cloth C (Fig. 2) or.other filtering material. The drum may be divided into a plurality of sectors, as is customary in the art, to each of which suction or pressure may suitably be applied through a regulating valve IS. A vacuum hose 20 and a compressed air pipe 2! communicates with the valve, which controls the application of suction or pressure through the pipes 22 which terminate in various sectors of the drum. It is understood that the drum i8 is revolved by gear 23 and worm 24 through the slip in the tank, and the suction will pick up the clay in the form of a cake on the periphery of the drum, the filtered liquid being drawn off in a known manner. Near the end of the travel of the drum, the suction may be replaced by pressure for assisting in the removal of the cake; as hereafter described.

As illustrated, the exposed portion of the filter surface of the drum i8 is encased in a hood or other stationary member 25 which is suitably spaced from the drum so as to form a passageway 26 therewith.- A series of baffles 21 may be disposed in said passageway for directing air toward the drum. At spaced points along the hood, means are provided for admitting and withdrawing airbeneath the hood. For example, a heated air conduit 28 (Figs. 1 and 2) communicates with the hood 25 at one side of the drum, while conduit l2 of the slip preheater, connects with the air passageway at the other side. Any suitable means may be provided for supplying heated air or gases to conduit 28, which may be driven through the hood and to the slip preheater by any suitable means such,- as fan 29, and regulated by gate 29A. Should the natural draft of the flue l3 be insufficient to maintain the heated air in circulation from conduit 28, through the hood, through conduit I2 and the stack, any suitable means, such as a fan or the like, may be supplied in the fiues l3, or I3A, as auxiliaries.

In use, the heating of the slip or sludge precedes the filtering operation. It is estimated that this preliminary treatment of the slip during which its temperature is raised to approximately 140 F. will raise the density of the sludge and thereby increase the capacity of the filter to a marked degree. The sludge or thickened slip containing about 30 to 40 percent of solids reaches the pipe 8 from a pump 4 (Fig. 1) which draws its supply from the feed well 3. The slip inthis well is kept at a constant level by a float valve 2 that regulates the incoming slip provided from the previous unit, such as a Dorr thickener, through pipe I as set forth in my aforementioned patent. From pipe 8 the slip is passed into the top of the cylinder or stack 5, whence it falls through successive cascades which retard itsgravitation, while exposed to the ascending heated air supplied through conduit i2. The hot air current which preferably constitutes the hot air discharged from the filter hood, has a temperature of substantially 190-F. which has been found to be adequate in the heat interchanger, to

raise the slip to approximately to F. which appears to be the most efiicient operating temperature for the filtering stage. The general 1 direction of the slip is indicated in the drawings in dash lines, while arrows mark the travel of the air currents. Although not shown in the drawings, it is understood that the slowly descending slip and ascending air are intimately exposed for effecting the heat transfer.

The heated slip or sludge now passes by pipe ii, to the tank or well l5 where it may be maintained, if desired, by overflow pipe i1, at'level A. In order to keep the slip at 120 to-140 F. it is often necessary to add steam or heated air or gases into well l5. This is done through several openings |5A at the bottom of the well so that the heat will circulate equally throughout the contents of well l5. In this unit the filtering of the heated slip transpires, the filter drum I8 is revolved in a clockwisedirection at a speed of approximately one revolution in twelve minutes. For the major portion of this travel, the regulating valve i9 establishes communication between the vacuum line 20 and the pipes 22, so that suction is applied to the under face of the filter cloth C. As each sector of the drum passes through the tank or well IS, the suction imposed on the filter cloth causes extraction of some of the water from the slip with the attendant deposit of a clay cake about onesixteenth to one-eighth of an inch thick on the periphery of the drum.

The suction in pipes 22 is maintained as the sector of the drum emerges from the well IS. The clay cake on the drum thereupon becomes exposed to the heated air or gas current in the hood 25, and is slowly moved in a clockwise direction. as the hot air current passes in a direction counter thereto. The baffles 21 are slightly inclined so that they direct the air toward the drum, whereby it impinges the outer face of the cake. These bailles may not be needed in some instances and can be omitted. Furthermore, the .hot air currents may be passed over the cake in the direction of its travel, without departing from the scope of the invention. During this phase of the operation, the under face of the cake is subjected to suction for the further extraction of moisture-while the outer face of the cake is subjected to the heated air and gases, a portion of which is drawn into or through the interstices of the clay cake 'for further heating and drying.

The heated gases are supplied by a hot air furnace or other heater and are propelled therefrom through conduit 28 by fan 29 at a regulated speed, adjusted by gate 29A to properly treat the volume of clay filtered. Upon leaving the furnace, the air may be about 200 F. if used only for the filter, or filter and preheater. When the hot air and gases are used for the drying units as well (shown in Figs. 1 and 4) they may be heated to 300 and up to 600 F., and over, when traveling with the cake to be dried, and then returned to the filter hood at about 200 F. and for recirculating through the furnace 31. For a '75 ton clay capacity unit when the fan is properly regulated in speed and volume for delivering approximately 1700 cubic feet perminute to the hood, the temperature of the air propelled through the hood 25 is kept at about 200 F. From thence it goes through the conduit or pipe l2 (Fig. 1) to the preheater, and is ex- 7 hausted to the atmosphere or used further in a condenser to save the water.

Referring again to the clay cake on the drum periphery, the heating and drying with the concurrent application of suction presents a com- 75 bined treatment which increases the emciency of the unit for clay filtering, and facilitates removal of the cake from the drum. It is well known that clay possesses peculiar adhering qualities, and displays an amnity for filter cloth and the like. However, in the practice of themesent methods, the clay cake has been removed from the drum with marked success. This may be attributed, in-part, to the application of heat to the slip as well as to the cake. It is probable, that the suction of the heated air through the cake, not only dries and heats the latter, but has a similar efiect on the filter cloth so that any film of moisture betweenthe face of the cake and the cloth is removed.

.The heating and drying of the filter cloth and cake continues as the sector of the drum approaches the inlet of the hood. At this point a scraper-3i! (Figs. 1 and 2) or doctor roll 30A (Fig. 4.) or any other suitable mechanical means is provided for removing the cake from the drum. Furthermore, the regulating valve is, automaticallycuts oil the vacuum connection, and air under pressure is thereupon admitted to pipes it. 'This air pressure is directed against the under face of the filter cloth and cake, while the outer face of the cake is still subjected to heated air. These factors cooperate with the mechanical scraper 3B or doctor roll 30A for speedily and emciently removing the cake from the drum, whence it is discharged onto a wire mesh belt conveyor 3! for distribution onto a dryer belt 35 or into a screw conveyor 32 (Fig. 2),

or other suitable means for passage to the next unit, such as a rotary drier, or some other type of suitable drier. Toprevent'spill an apron 33 is placed at a, steep angle between the drum discharge beneath the scraper or doctor roll and belt 3i to catch small particles and deliver them onto the final conveyors. When the dryer belt combination is used; a. butterfly bailie 35 (Figs. 1 and 5) should be placed between the 200 F. air and the 300 5}, or hotter, air passages to keep them from commingling. This butterfly valve is made to revolve at a slightly faster speed than the traveling cake passing the lip of the scraper 38.

At the end of the filtering operation, the filter cake together with clay particles lodged in the meshes of the filter, in the apparatus employed, is approximately "Iii percent solids and 30 percent water. This is made possible by the preheating of the thick slip before passing it to the filter and the further heating and drying of the cake while it passes up and around under the hood. The heating of the slip accelerates filtration of the water, tends to keep the filter meshes clear and to prevent too close adherence of the solids to the filter, while the heating of the cake above the liquid level not only dries the cake and renders it more firm in consistency, but makes its se aration from the filtering medium easier.

After the removal of the cake, when air pressure is used, it blows the cloth clear of any remaining particles, and as the drum sector passes below the level of the liquid in well 15, the air pressure is automatically turned oh and the suction turned on by valve is, so that as the sector submerges, another filtering operation begins. While the operationhas been described as applied to a sector of the drum, it is understood that the entire circumference of the drum functions, in like manner.

It is apparent that the provision of air pressure and/or a mechanical scraper for either individually or jointly removing the cake from the filtering medium is illustrative only. One or both may be discarded in favor of other suitable means for removing the cake and cleaning 5 the filter medium. Various other arrangements for performing these functions may accordingly be adopted without departing from the scope of the improvements.

Referring to Figures 1 and 4, alternate types of conveyor and drier are illustrated. These have .beendeposited thereon from the filter drum. As illustrated, the heated air passes from the tunnel to the hood and thence over the filter drum and to the preheater. The cakes are conveyed along the tunnel in a direction with- (as shown in Fig. l) or counter to (shown in Fig. 25 4) the blast of heated gases passing therethrough, so that they are exposed on both faces to the heating and drying action of the gases. If this combined form of filter and drier is-not used, the cake may be conveyed to a rotary type l of drier or some other drier suitable for the purpose.

Referring more particularly to the mechanical take off means illustrated in Figs. 1, 2, and 5, the scramr '30 preferably comprises an elongated blade of sheet iron or other suitable material. A hollow chamber til is provided beneath, the blade into which hot air and gases may be introduced through trimnion fill smut which the blade swings. Any suitable energized 49 means such as a. spring or a weight (not shown) may be employed for urging the blade against the drum during the filtering operation. The blade and cber dd extend along the face of the drum, so that the hot air and gases may be admitted at one end of the scraper, may circulate through chamber so, and be freed therefrom at the other end. If desired, a perforated pipe may serve the double function of introducing and freeing the air and gases to and from chamber 50, and may serve as trunnlons or bearings about which the blade may swing. The cake from the engages the hot plate of the scraper'sfl and slides over it onto the moving woven wire belt t! for delivery to the conveyor 32 or belt 35. The heated scraper facilitates removal of the cake from the drum.

Referring to Figs. 4 and 6, the doctor roll 3%. comprises a cylinder, extending along the face of the drum, having a plurality of radially extending flexible rubber ribs or fins which touch the drum l8 and conveyor 3i. This roll is equippad to revolve at a speed slightly in excess of that of the drum to facilitate transfer of the cake to conveyor 3!, which in turn is equipped to travel slightly faster than the doctor roll.

Various modifications of the apparatus as well as of the methods will be apparent to those skilled in the art and may be made without departing from the scope and purview of the improvements. For example, the improvements may be practiced irrespective of the type of filter medium employed. The filtering surface may be fiat or curved and the deposit or cake formed on w the convex or concave face without departing from the invention.

I claim:

1. The process of treating a slip or sludge composed of clay and water for separating the solid particles from the liquid comprising the steps of cascading the slip, and concurrently subjecting the slip to heated air, filtering the slip thus heated and thereby forming a cake of the clay particles, subjecting the cake to heated air during the filtering step, and positively removing the cake from the filtering media.

2. Means for treating and filtering clay slip comprising a vertical stack having stationary cone shaped bellies, a set of cones in juxtaposition to said baflles, an inlet port for clay slip at the top of said'stack for discharging slip downward about said battles and cones, an outlet from the bottom of said stack, a well communicating with said outlet, a filter drum suspended in said well and projecting above same, a stationary hood spaced from the exposed face of said drum, and forming an air passage therewith, a conduit establishing communication between said air passage and the bottom of the stack, and means for circulating heated air in said hood and stack.

3. Means for treating and filtering clay slip comprising a vertical stack having stationary cone-shaped baiiies, a set of revolving cones in juxtaposition to said bailies, an inlet port for clay slip at the top of said stack for discharging slip downward about said bailies and cones, an outlet from the bottom of said stack, a covered well communicating with said outlet and provided 'moving the deposit from the medium,

with heater inlets for am or hot air, a filter drum suspended in said well and projecting above same, .a stationary hood spaced from the exposed face of said drum, and forming an air passage therewith, a conduit establishing communication between said air passage and the bottom of the stack, and means for circulating heated air in said hood and stack.

4. Means for treating and filtering clay slip comprising a stack,- means for feeding clay slip to said stack, an outlet for said stack, a receptacle communicating with said stack, means for filtering the slip fed from the stack to the receptacle, a source of heated air, and means for directing heated air from said source over said filter cake and into said stack.

5. Means for treating and filtering clay slip comprising a stack, means for feeding clay slip to said stack, an outlet for said stack, a receptacle communicating with said stack, means for filtering theslip fed from the stack to the-receptacle, a drier, means for transferring the filter cake from thefiltering means to the drier, a source of heated air, and means for directing heated air from said source to said drier, filtering means and stack.

6. In a filter, the combination 01' a filter medium and a heated mechanical scraper for resaid scraper having a chamber and means for introducing heated air into said chamber for heating said scraper.

DAVID F. MCCORMICK. 

